The question of how best to reduce the levels of particulate matter expelled to atmosphere in the exhaust gases of automotive diesel engines is currently of considerable interest. In this connection, it is desired to develop efficient and practical devices and methods for removing substantial portions of particulates from the exhaust gases in diesel engine exhaust systems before permitting the exhaust gases to escape to atmosphere.
It is recognized that, to be successful, a diesel engine exhaust particulate trap must have certain characteristics, some of which are (1) chemical stability at the maximum operating temperatures encountered in the engine exhaust system (2) adequate thermal shock resistance to withstand frequent and irregular temperature changes recurrent in exhaust systems during vehicle operation and (3) capabiity of being packaged in a suitable manner to avoid failure due to vibration and other stresses encountered during vehicle operation. Certain ceramic materials have been found to meet the above criteria adequately, as is shown by their use in catalytic converters used for exhaust emission control in gasoline powered vehicle engines. Thus, it has been proposed to utilize porous walled ceramics of the type used for monolithic engine exhaust catalyst devices in making filter elements for diesel exhaust particulates.